Process for the polymerization of ethylene and catalytic component therefor

ABSTRACT

A catalytic component having controlled structure for use in combination with a cocatalyst for the polymerization of ethylene, and being the product of the process of subjecting a component consisting essentially of titanium, magnesium, and chlorine to a reduction treatment and after such treatment contacting the component with a transition metal chlorine-containing compound and process of polymerizing ethylene using such catalytic component to produce polymers having a broad molecular weight distribution.

This application is a continuation, of application Ser. No. 07/755,878,filed Sep. 4, 1991, now abandoned, which is a division of applicationSer. No. 07/436,059, filed Nov. 13, 1989, now U.S. Pat. No. 5,151,396.

BACKGROUND OF THE INVENTION

The present invention pertains to a process for the polymerization ofethylene for obtaining a polymer with a broad molecular-weightdistribution. Specifically, the objective of the invention is to obtainhigh and low density linear polyethylene. The result is obtained due tothe particular treatment, prior to its use with a cocatalyst in thepolymerization of the ethylene, of the catalytic component. Prior to itsuse, the catalytic component comprising at least one magnesiumderivative and a chlorine-containing derivative of titanium mainly atthe oxidation state 3 and/or 4 undergoes a reduction by a metalliccompound possessing at least one metal-carbon or metal-hydrogen bond,followed by a treatment by a transition metal halogen compound.

The invention also pertains to the process for treating the catalyticcomponent.

As used herein the phrase "polymerization of ethylene" means not onlythe homopolymerization of the ethylene, but also the copolymerization ofthe ethylene with an alpha-olefin, such as propylene, 1-butene or1-hexene.

The polymers with a broad molecular-weight distribution, industriallyemployed in particular in extrusion-blow molding techniques, aredistinguished by their polydispersity and their fluidity index from thepolymers with a narrow molecular-weight distribution, industriallyemployed, in particular, for injection molding.

The polymers with a narrow molecular-weight distribution possess, on anaverage, a polydispersity of about 4 to 6, the polydispersity being theratio of the molar weight by weight to the molar weight by number. Thesepolymers with high fluidity posses a fluidity index ratio MFR₅₋₂ lessthan 3.3, MFR_(5`) being, according to the ASTM standard D1238, the MI₅/MI₂ ratio of the fluidity index under 5 kg to the fluidity index under2.16 kg; the MFR₂₁₋₅ ratio of the fluidity indices under 21.6 kg to thefluidity index under 5 Kg, MI₂₁ /MI5 according to the ASTM standard D1238, is less than 10. These products are obtained in a single reactorby the polymerization of the ethylene in suspension in solution, or inthe gaseous phase in the presence of a specific Ziegler-type catalystcomprising a cocatalyst, in general an alkylaluminum, and a catalyticcomponent containing Ti, Mg, Cl and possibly an electron donor. Theproducts obtained with a narrow distribution possess a limitedelasticity which avoids the very negative phenomenon of injectionshrinkage.

Due to their lack of elasticity, these products are unsuitable fortechniques requiring a high mechanical resistance in the melted state,as, for example, in the case of extrusion-blow molding. When theseproperties are in demand, one employs polymers with a broadmolecular-weight distribution, preferably possessing a fluidity indexratio MFR₂₁₋₅ greater than 16 for a fluidity index MI₅ of about 1 to1.5, or a MI₅ /MI₂ ratio greater than 3.5 for MI₂ >1.

The industrial manufacture of these products in a single reactorpresents great difficulties in the presence of a Ziegler-type .catalyst.

According to Zucchini; U. and G. Cecchin: "Control of Molecular-WeightDistribution in Polyolefins Synthesized with Ziegler-Natta CatalystSystems," Adv. in Polymer Science 51, 101-153 (1983), a document whichreflects the prior art in this matter, the best means for obtaining apolymer with a broad molecular-weight distribution in the presence of aZiegler-type catalyst is to carry out the polymerization in severalstages or in a series using at least two successive reactors. However,even under these best conditions, it is not easy to manufacture apolyethylene with a MFR ₂₁₋₅ greater than 16, a necessary conditionbeing to proceed with catalysts that yield broad distributions in asingle reactor. Moreover, this process presents the disadvantage orrequiring at least two reactors which leads to a loss in productivitywith regard to the significance of the installation and a delicatecontrol due to the activity of several reactors instead of just one.

According to FR-A-2,596,398, it is possible to obtain, by thepolymerization of ethylene in a single reactor, a polymer with a broadmolecular-weight distribution with a MFR MI₂₁ /MI₅ greater than 16.obtain this result, a mixture of MgCl₂ and TiCl₄ obtained by jointpulverization is employed as the catalytic component. In addition to thejoint pulverization of the components, which requires industriallycomplex rules, the process presents the disadvantage of using acomponent with a poorly defined structure, which leads to themanufacture of a polymer with a heterogeneous granular distribution.

SUMMARY OF THE INVENTION

The advantage of the process of this invention is that it uses acatalytic component with a controlled structure, capable ofmanufacturing a polymer with a broad molecular-weight distribution, theMI₂₁ /MI₅ ratio being greater than 16 and possibly exceeding 25 forproducts with high molecular weight, in particular for products, thefluidity index MI₂ of which is less than 0.5 and the MI₅ /MI₂ ratiobeing greater than 3.5. Moreover, the performances of the componentobtained according to FR 2,596,398 are improved.

To obtain these results, the ethylene is polymerized in the presence ofa catalyst comprising a cocatalyst selected from among thealkylaluminums and of a catalytic component based on at least Mg, Ti andCl treated under the conditions set forth below.

DETAILED DESCRIPTION

The characteristic of the invention consists, in a first stage, ofsubjecting the catalytic component to a reducing treatment, then in asecond stage, treating the product obtained with a transition metalchlorine-containing compound.

The initial catalytic compound before treatment is a product that isknown in itself and is extensively described in the literature. It isusually the result of the combination of at least one titanium compound,one magnesium compound, one chlorine compound and possibly an electrondonor or acceptor and any other compound that can be used in these typesof components.

The titanium compound is usually selected from among the compoundshaving the formula Ti(OR)_(x) Cl_(4-x), in which:

(i) R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, or COR¹with R¹ being a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, and

(ii) x is a number from 0 to 3.

The magnesium compound is usually selected from among the compoundshaving the formula Mg(OR²) n^(Cl) _(2-n), in which R² is hydrogen or acyclic or linear hydrocarbon radical and n is a number less than orequal to 2.

The chlorine can result directly from the halide of titanium and/or thehalide of magnesium, but it can also result from an independentchlorinating agent such as hydrochloric acid or an organic halide suchas butyl chloride.

The optional electron donor or acceptor is a liquid or solid organiccompound known for entering into the composition of these catalyticcomponents. The electron donor can be a mono- or polyfunctional compoundadvantageously selected from among aliphatic or aromatic carboxylicacids and their alkyl esters, aliphatic or cyclic ethers, ketones, vinylesters, acrylic derivatives, in particular alkyl acrylates ormethacrylates and silanes. Compounds such as methyl paratoluate, ethylbenzoate, ethyl or butyl acetate, ethyl ether, ethyl paraanisate,dibutylphthalate, dioctylphthalate, diisobutylphthalate,tetrahydrofuran, dioxane, acetone, methyl isobutyl ketone, vinylacetate, methyl methacrylate and silanes such as phenylteiethoxysilane,aromatic or aliphatic alkoxysilanes are especially suitable as electrondonors.

The electron acceptor is a Lewis acid preferably selected from amongaluminum chlorides, boron trifluoride, chloranil or alkylaluminums andalkylmagnesiums.

The catalytic component is used in the form of a complex of at least Mg,Ti, Cl, the chlorinated titanium being mainly in the form of TI^(IV),Ti^(III) or a mixture of both, optionally with an electron donor oracceptor. The catalytic component can be in the form of a complex, butalso in the form of a deposit on a mineral support such as SiO₂ or Al₂O₃ or an organic support, for example, of the polymer type.

In a first stage, the catalytic component as defined above is treatedwith a reducing agent. It involves a compound that is gaseous, liquid orsoluble in hydrocarbons, capable, as it is generally known in chemistry,or reducing the degree of oxidation of the Ti^(IV) and/or Ti^(III). Thereducing agent employed is preferably a metallic compound possessing atleast one metal-carbon or metal-hydrogen bond. The metallic usuallyselected from among the compounds MQ_(y) Cl_(z-y), M compoundspossessing at least one metal-carbon bond are being a metal of groups I,II and III of the Periodic Table, and more particularly, Al and Mg; Qbeing a cyclic or linear hydrocarbon radical, z being a numbercorresponding to the maximum valence of the metal; and y being a numberless than or equal to z. Also included in the definition of thesecompounds are the addition products of these compounds betweenthemselves such as, for examples: NaAl(C₂ H₅)₄ or the products obtainedby bridging two metallic compounds defined above by an oxygen such as,for example, aluminoxanes and aluminosiloxanes. Among these metalliccompounds, one prefers aluminoxanes, aluminosiloxanes, dialkylmagnesiumsand alkylaluminums of the type Al(R³)_(c) X_(d) where

(i) X is Cl, and

(ii) R³ represents a C₁ to C₁₄ saturated hydrocarbon radical, or (OR₄)with R⁴ which is a C₁ to C₁₄ saturated hydrocarbon radical with 0≦d≦1.5and c+d=3.

Al(C₂ H₅)₃, Al(C₂ H₅)₂ Cl, Al(C₄ H₉)₃, Al₂ (C₂ H₅)₃ Cl₃, Al(C₆ H₁₃)₃,Al(C₈ H₁₇)₃ and Al(C₂ H₅)₂ (OC₂ H₅) can be cited as examples.

The metallic compounds possessing at least one metal hydrogen bond areusually selected from among the compounds MQ'_(c) X_(d) H₃ where M is ametal as defined above, Q' is a cyclic or linear hydrocarbon radical, Xis Cl or is selected from among the preceding Q' radicals with 0≦d≦1.5,1≦e≦z and c+d+e=z, z corresponding to the maximum valence of M. Hydridessuch as Al(C₄ H₉)₂ H, Al(C₂ H₅)₂ H, (C₂ H₅)₄ B₂ H₂ and mixed hydridessuch as aluminum-lithium, AlLiH₄, can be cited among these compounds.The combination of the hydrides with one another or with theorganometallic compounds defined above is obviously possible.

In this stage, the component is treated under an inert atmosphere withthe reducing agent, as is, or in the presence of a diluent both assolvent of the reducing agent and inert to it as well as to thecomponent. The hydrocarbons among others are suitable for thisapplication. Even though the reaction temperature is not critical, forreasons of reasonable reaction duration, the reduction is preferablycarried out from ambient temperature to 150° C. under atmosphericpressure or under pressure, preferably between 40° and 100° C. underatmospheric pressure for reaction durations of about ten minutes to 24hours.

The reduction reaction is stopped when at least 50% by weight of theinitial titanium has its degree of oxidation reduced by at least oneunit, for example, when 50% of the Ti^(IV) is reduced to Ti^(III) or 50%of the Ti^(III) is reduced to Ti^(II). However, it is preferable tocontinue the reduction of titanium as much as possible, but it isrecommended to stop the reduction when the mean degree of reduction ofthe titanium is closest to II. In this reduction stage, the molar ratioof reducing-agent metal to titanium is preferably greater than two andespecially between 10 and 50.

The reduction reaction is stopped by cooling and washing the productobtained, preferably with a hydrocarbon, to eliminate the excessreducing agent. The resulting product can be dried.

In the second stage, the reduced product obtained is treated with atransition metal chlorine-containing compound. This chlorine-containingcompound is most often a chloride, an alkoxychloride or an oxychlorideof a transition metal selected from among titanium, vanadium, chromium,zirconium such as, for example, TiCl₄ or VCl₄. To facilitate thechlorination reaction, it is preferable to employ a chlorine-containingcompound that is liquid or is soluble in a solvent that is inert to theproducts brought into contact. The treatment is carried out by bringinginto contact, in an inert atmosphere, the reduced product of the firststage with the chlorine-containing compound. The contact temperature,once again, is not critical. For practical reasons, it is recommended totreat the products in contact at a temperature ranging between theambient temperature and 150° C. and preferably between 60° and 100° C.for treatment durations ranging between several minutes and four hours.The amount of transition-metal chlorine-containing compound used ispreferably at least half of the stoichiometry, especially close to thestoichimetry or in excess with regard to the titanium content of theproduct obtained at the end of the first stage. After treatment, thecomponent is finally recovered under an inert atmosphere after washingand optionally drying.

The catalytic component obtained after these two treatment stages isemployed in the classical manner with a commonly known cocatalyst,generally selected from among the alkylaluminums, in the suspension orgaseous-phase polymerization processes of olefins.

In a suspension polymerization process of ethylene, one operates in theusual manner in a liquid hydrocarbon medium at temperatures capable ofreaching up to 120° C. and under pressures capable of reaching up to 250bars.

The gaseous-phase polymerization of ethylene in the presence of hydrogenand inert gas can be carried out in any reactor capable of gaseous-phasepolymerization and in particular in an agitated-bed or fluidized-bedreactor. The implementation conditions are known from the prior art andare conventional. One generally operates at a temperature lower than themelting point Tf of the polymer or copolymer to be synthesized and moreparticularly between 20° C. and (Tf -5° C.) and under a pressure suchthat the ethylene and possibly the other hydrocarbon monomers present inthe reactor are essentially in vapor phase.

The polymerization can be carried out in two stages. In a first stage,it is possible to consolidate the catalytic system by carrying out aprepolymerization based on ethylene in the presence of the constituentsof the catalytic system and a cocatalyst, then in a second stage, bycontinuing the polymerization by adding ethylene or a mixture ofethylene and an alpha-olefin such as mentioned above. Theprepolymerization stage produces a polymer formation not exceeding 10%by weight of the total polymer becoming formed. This prepolymerizationstage is carried out in suspension in the presence of a hydrocarbondiluent, in the gaseous phase or in a combination of suspension andgaseous phase.

The invention will be further described in connection with the followingexamples which are set forth for purposes of illustration only.

EXAMPLE 1

a) Preparation of the Catalytic Component

8.3 g of anhydrous MgCl₂ are pulverized for six hours; 0.7 mL of TiCl₄is added and the mixture is pulverized for four hours. The solidrecovered is extracted from the pulverization bowl with heptane anddried under vacuum. A product A containing 3% by weight of titanium isobtained. Four grams of A are treated in heptane with triethylaluminumat the concentration of 0.85 M/l (Al/Ti=14) for three hours at 80° C.The solid obtained is rinsed three times, protected from air, with 50 mlof heptane and is dried under vacuum. The product recovered is broughtinto contact, protected from air, with 40 ml of TiCl₄ for four hours at100° C. After five washings with heptane, the solid obtained is driedunder vaccum. A solid B containing 4.4% by weight of titanium and 0.9%by weight of aluminum is obtained.

b) Polymerization of Ethylene in Suspension

The catalytic component B is used for the polymerization of ethylene insuspension. In a stainless steel 2.5-liter reactor provided withagitation by a blade turning at 650 rpm, one introduces in the followingorder at ambient temperature under an inert atmosphere: one liter ofheptane, trihexylaluminum (3 mM) and the catalytic component B in anamount corresponding to 2.5 mg of Ti.

Hydrogen is added up to a partial pressure of 4.3 bars (test 1) and 5bars (test 2), and one completes 10 with the ethylene by adjusting thepressure to reach 9 bars absolute of total pressure after heating at 80°C. This total pressure is kept constant for one hour by adding ethylene.

After one hour, one stops the injection of ethylene, one cools atambient temperature, the catalyst is deactivated by adding a methanolsolution slightly acidified by 10% hydrochloric acid. The polymersuspension is filtered and then dried.

By way of comparison, test 1 is repeated with the product A.

The results obtained on the final polymer are follows:

    ______________________________________                                                        Productivity                                                  Com-            in g of PE/g of       MI.sub.21 /                                                                         MI.sub.5 /                        ponent                                                                              TEST      component   MI.sub.5                                                                           MI.sub.21                                                                          MI.sub.5                                                                            MI.sub.2                          ______________________________________                                        B     1         2,800       0.5  13    26   NS                                A     1           775       0.87 14.2  16.3 NS                                      comparison                                                              B     2         1,500       4.3  NS    NS   5                                 ______________________________________                                         NS = not significant. Either I.sub.2 is too low to be measured or I.sub.2     is too high to be measured correctly.                                    

EXAMPLE 2

a) Preparation of the Catalytic Component

The component C is prepared under the conditions for obtaining thecomponent A in Example 1, except for the duration of joint pulverizationwhich is eight hours.

Amount of anhydrous MgCl₂ : 10 g

Amount of TiCl₄ : 0.66 ml

A product C containing 2.5% by weight of titanium is obtained.

On the one hand: 3.6 g of solid C are treated in heptane with ClAl(C₂H₅)₂ at the concentration of 0.7 M/l (Al/Ti=17.7) for two hours at 80°C. After four washings each with 60 ml of heptane protected from air,the solid is brought into contact with 30 ml of TiCl₄ for two hours at100° C. After washings with heptane and drying under vacuum, the solid Dcontaining 3.8% by weight of titanium and 0.8% by weight of aluminum isobtained.

On the other hand: 3 g of solid C are treated in heptane withtriethylaluminum at the concentration of 1.2M/l (Al/Ti=15) for two hoursat 80° C. After washings with heptane and drying under vacuum, the solidis brought into contact with 30 ml of TiCl₄ for two hours at 100° C.After washings with heptane and drying under vacuum, the solid Econtaining 11.5% by weight of titanium and 1.5% by weight of aluminum isobtained.

b) Polymerization of Ethylene in Suspension

The components D, E and C, by way of comparison, are each used in thehomopolymerization of ethylene under the condition in Example 1 exceptthat pertaining to the hydrogen pressures.

The results obtained for the final polymer are as follows:

    ______________________________________                                                H2        Productivity                                                        pressure  in g of PE/G of        MI.sub.21 /                          Component                                                                             in bars   component   MI.sub.5                                                                            MI.sub.21                                                                          MI.sub.5                             ______________________________________                                        D       4.3       2,500       0.77  18   23.4                                 E       4         1,100       0.60  13   21.7                                 C       4.3       2,500       1.33  22.8 17                                   ______________________________________                                    

EXAMPLE 3

a) Preparation of the Catalytic Component

10 g of anhydrous MgCl₂ and 1.15 ml of TiCl₄ are treated under thecondition of Example 1, except for the duration of joint pulverizationwhich is 16 hours.

The product obtained is treated in heptane with triethylaluminum at theconcentration of 0.5 M/l (Al/Ti =2) for two hours at 90° C. Afterwashing with heptane, the solid is treated with 1.5 ml of VCl₄ for 30minutes at 80° C. After washing with heptane and then drying undervacuum, a solid F containing 3.7% by weight of Ti, 4.4% by weight of Vand 1.72% by weight of Al is obtained.

b) Copolymerization of Ethylene and 1-Butene in Vapor Phase

For the vapor-phase polymerization, one employs a stainless-steel 2.5liter, spherical reactor, provided with agitation by a blade turning at250 rpm. The temperature is regulated at 85° C. At 85° C., oneintroduces into the reactor the reagents in the following order:trihexylaluminum (0.7 mM), butene up to a partial pressure of 1.8 bars,ethylene 8.2 bars and hydrogen 2 bars.

The component F, in an amount corresponding to 2.5 mg of Ti, is injectedinto the reactor, the total pressure (12 bars) is kept constant bycontinuously adding an ethylene-butene mixture with 3.7 mol % butene.After one hour of reacting, the reactor is degassed and cooled; onerecovers a polymer powder with a composition of 17.8 ethyl branchingsper 1,000 carbons. The other characteristics are as follows:

    ______________________________________                                                  Productivity in g of                                                          polyethylene per g                                                  Component of component    MI.sub.2                                                                             MI.sub.5 /MI.sub.2                           ______________________________________                                        F         3,000           1.54   4.9                                          ______________________________________                                    

EXAMPLE 4

a) Copolymerization of Ethylene and 1-Butene in Vapor Phase

The component E of Example 2 is used in the copolymerization of ethyleneand butene under the same conditions as in Example 3, except for thepartial pressure of hydrogen 7.5 bars, partial pressure of butene 0.8bar and partial pressure of ethylene 4.2 bars. The temperature isregulated at 65° C. and the composition of the ethylene-butene gaseousmixture feeding the reactor is 3.54 mol % of butene.

By way of comparison, the test with the component C is repeated:

    ______________________________________                                                  Productivity in g of                                                          polyethylene per g                                                  Component of component    MI.sub.2                                                                             MI.sub.21 /MI.sub.2                          ______________________________________                                        E         1,500           1      65                                           C         2,000           1.8    35                                           ______________________________________                                    

EXAMPLE 5

A solution of dibutylmagnesium 0.5 M/l, tetraisobutyaluminoxane 0.015M/l and disecbutyl ether (EDSE) 0.03 M/l is introduced into a reactorunder inert atmosphere. This solution is maintained under agitation at50° C. for about 16 hours. One then slowly adds into the reactor amixture of tertiobutyl chloride (tBuCl) in an amount such that thetBuCl/l Mg weight ratio=3 and disecbutyl ether in an amount such thatthe EDSB/Mg weight ratio=0.6 at the end of the addition. The temperatureand the agitation are maintained for three hours. The solid obtained isfiltered and washed with hexane and then returned to suspension inhexane. Anhydrous HCl is bubbled for 30 minutes at ambient temperature.After washing and filtration, the solid is returned to suspension inTiCl₄ and maintained at 90° C. for two hours. After filtration, washingand drying under inert atmosphere, a component G with sphericalmorphology containing 3.1% by weight of titanium is obtained.

The catalytic component G is treated in heptane with triethylaluminum atthe concentration of 600 mM/l, with an Al/Ti molar ratio=23, for onehour at 60° C. After washing with heptane and drying in an inert medium,the intermediate solid obtained is treated with TiCl₄ at 90° C. for twohours. After washing and drying in an inert medium, the component Hobtained has preserved its spherical morphology and possesses a titaniumcontent of 7.3% by weight.

b. Polymerization of Ethylene in Suspension

The component H is used in the polymerization of ethylene in suspensionunder the conditions of Example 1 except for the cocatalyst:triisobutylaluminum 2.5 mM/l, diluent: hexane, temperature: 75° C.,partial pressure of hydrogen: 4.2 bars: partial pressure of ethylene:6.4 bars: and duration of the polymerization: three hours.

By way of comparison, the test with the component G is repeated. Theresults obtained are as follows:

    ______________________________________                                                Productivity                                                                  in g of                                                                       PE/G of                                                               Component                                                                             component   MI.sub.5                                                                             MI.sub.21                                                                           MI.sub.21 /MI.sub.5                                                                   MV.sub.A                             ______________________________________                                        G       12,000      1.2    14.1  11.7    0.4                                  H       17,000      1      24    24      0.42                                 ______________________________________                                    

EXAMPLE 6

a) Preparation of the Catalytic Component

The catalytic component G is treated in heptane with dibutylmagnesium150 mM/l, with a Mg/Ti molar ratio=5, for two hours at 80° C. Afterwashing and siphoning the solvent, the intermediate solid is treatedwith TiCl₄ at 90° C. for two hours. The component I obtained afterwashing and drying has preserved a spherical morphology and contains3.9% by weight of titanium.

b) Polymerization of Ethylene in Suspension

The catalytic component I is used in the polymerization of ethyleneunder the conditions of Example 5. By way of comparison the resultsobtained with component G are repeated.

    ______________________________________                                                Productivity                                                                  in g of                                                                       PE/g of                                                               Component                                                                             component   MI.sub.5                                                                             MI.sub.21                                                                           MI.sub.21 /MI.sub.5                                                                   MV.sub.A                             ______________________________________                                        G       12,000      1.2    14.1  11.7    0.4                                  I       17,900      1.3    22.8  17.5    0.4                                  ______________________________________                                    

EXAMPLE 7

a) Preparation of the Catalytic Component

The catalytic component J is prepared in a similar manner to thecatalytic component G in Example 5. The component J has a sphericalmorphology and contains 1.6% by weight of titanium.

The catalytic component J is treated in heptane with diethylaluminumhydride at the concentration of 80 mM/l and an Al/Ti molar ratio=2.5 fortwo hours at 80° C. After washing and siphoning the solvent, theintermediate solid is treated with TiCl₄ at 90° C. for two hours. Thecomponent K obtained after washing and drying possesses the followingcharacteristics: Ti=5.7% by weight and spherical morphology.

b) Polymerization of Ethylene in Suspension

The components J and K are used in the polymerization of ethylene underthe conditions of Example 5.

    ______________________________________                                                Productivity                                                                  of g of                                                                       PE/g of                                                               Component                                                                             component   MI.sub.5                                                                             MI.sub.21                                                                           MI.sub.21 /MI.sub.5                                                                   MV.sub.A                             ______________________________________                                        J       17,700      1.15   13.2  11.4    0.42                                 K       26,400      0.48   7.8   16.2    0.4                                  ______________________________________                                    

While the invention has been described in connection with a preferredembodiment, it is not intended to limit the scope of the invention tothe particular form to set forth, but on the contrary, it is intended tocover such alternatives, modifications, and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

What is claimed is:
 1. A process for the homopolymerization of ethyleneor the copolymerization of ethylene with an alpha-olefin, in suspensionor in the gaseous phase, to form a polymer having a broad molecularweight distribution, a MI₂₁ /MI₅ ratio greater than 16, MI_(z) less than0.5, and a MIS/MI₂ ratio greater than 3.5, comprising carrying out thepolymerization in the presence of a catalyst comprising a cocatalyst anda catalytic component, said catalytic component prepared by combining achlorinated titanium compound mainly at the oxidation state of 3 and/or4 and having the formula:Ti(OR)_(x) Cl_(4-x) ' in which:(i) R is a C₁ toC₁₄ aliphatic or aromatic hydrocarbon radical, or COR¹ with R¹ being aC₁ to C₁₄ aliphatic or aromatic hydrocarbon radial, and (ii) x is anumber from 0 to 3, a magnesium compound and a chlorine compound,treating said solid component with a reducing agent capable of reducingthe degree of oxidation of Ti⁴ and/or Ti³ and after such treatmentcontacting the component with a chlorine-containing transition metalcompound consisting essentially of a chloride, an alkoxychloride or anoxychloride of a transition metal which is titanium, vanadium, chromiumor zirconium.
 2. The process of claim 1 wherein the cocatalyst is analkylaluminum compound.